1. Field of the Invention
The present invention relates to a resist underlayer film used in a lithography process during the production of a semiconductor device and to a forming method of a resist pattern using the resist underlayer film.
2. Description of the Related Art
In the production of a semiconductor device, fine processing by lithography using a photoresist is performed. The fine processing is a processing method for forming fine convexoconcave corresponding to a pattern on the surface of a substrate by: forming a thin film of a photoresist on a semiconductor substrate such as a silicon wafer; irradiating the resultant thin film with an activating light ray such as an ultra violet ray through a mask pattern in which a pattern of a device is depicted; developing the film; and subjecting the substrate to etching processing using the resultant photoresist pattern as a protection film. Recently, higher integration of devices has been pursued, and there is a tendency that exposure lights having shorter wavelengths such as a KrF excimer laser (having a wavelength of 248 nm) and an ArF exciter laser (having a wavelength of 193 nm) are adopted. However, these photolithography processes can cause a problem of lowering the dimensional accuracy of a photoresist pattern due to the influence of a standing wave caused by the reflection of exposure light on the substrate or the influence of the diffuse reflection of exposure light caused by unevenness of the substrate. In order to solve this problem, a method of providing a bottom anti-reflective coating between the photoresist and the substrate has been widely studied.
Such a bottom anti-reflective coating is formed typically by using a thermal crosslinkable composition in order to prevent intermixing between the bottom anti-reflective coating and a photoresist coated thereon. As a result, the formed bottom anti-reflective coating is insoluble in an alkaline developer used for developing a photoresist. Therefore, the removal of the bottom anti-reflective coating needs to be performed by dry etching prior to the processing of the semiconductor substrate (for example, see U.S. Pat. No. 6,156,479).
However, the photoresist is also dry etched in the removal process of the bottom anti-reflective coating by dry etching, which makes it difficult to keep the film thickness of the photoresist large enough for the processing of the substrate. This becomes a critical problem especially when a thin film photoresist is used to enhance the resolution.
In addition, as the ion implantation process in the production of semiconductor devices, a process for introducing impurity ions imparting a n- or p-conductivity type into a semiconductor substrate using a photoresist pattern as a mask may be adopted. In this process, to prevent the surface of a substrate from being damaged, it is not desired to perform dry etching in the formation of a photoresist pattern. Therefore, in the formation of a photoresist pattern for an ion implantation process, a bottom anti-reflective coating requiring the removal by dry etching cannot be used as an underlayer of the photoresist. A photoresist pattern used as a mask in an ion implantation process has had a relatively large line width and, therefore, been rarely influenced by a standing wave caused by the reflection of exposure light on a substrate or by the diffuse reflection of exposure light due to unevenness of a substrate. Therefore, problems of reflection have been solved by using a photoresist containing a dye or using a top anti-reflective coating on the photoresist. However, as the miniaturization has been advanced in recent years, fine patterns are required also for photoresists used in ion implantation processes, and providing a bottom anti-reflective coating (resist underlayer film) below the photoresist is required.
Under such circumstances, it has been desired to develop a bottom anti-reflective coating that can be dissolved in an alkaline developer used in the development of a photoresist and can be removed in the development process together with the photoresist. Such bottom anti-reflective coatings that can be removed in the development process together with the photoresist have been studied (for example, see Japanese Patent Application Publication No. JP-A-2004-54286, Japanese Patent Application Publication No. JP-A-2005-70154, International Publication No. WO 05/093513 pamphlet, International Publication No. WO 05/111719 pamphlet, International Publication No. WO 05/111724 pamphlet).
A bottom anti-reflective coating that can be removed in the development process together with a photoresist is exposed to a solvent when the photoresist is applied on the bottom anti-reflective coating. Through the exposure to a solvent, the solvent penetrates into the bottom anti-reflective coating, and thither, a photoacid generator component in the bottom anti-reflective coating is eluted. Therefore, in terms of the applicability to fine processing and the shape of a pattern to be formed, such bottom anti-reflective coating is not satisfactory.
Also disclosed is a photosensitive resin composition containing fluoroalkylcarboxylic acid sulfonium (see Japanese Patent Application Publication No. JP-A-2005-43883).